Four decades of geomagnetic and solar activity: 1960–2001

Vršnak

Veronig

et al. 2010

A&A

Context. Solar wind high-speed streams (HSSs), originating in equatorial coronal holes (CHs), are the main driver of the geomagnetic activity in the late-declining phase of the solar cycle. Aims. We analyze correlations between CH characteristics, HSSs parameters, and the geomagnetic activity indices, to establish empirical relationships that would provide forecasting of the solar wind characteristics, as well as the effect of HSSs on the geomagnetic activity in periods when the effect of coronal mass ejections is low. Methods. We apply the cross-correlation analysis to the fractional CH area (CH) measured between central meridian distances ±10• , solar wind parameters (flow velocity V, proton density n, temperature T , and the magnetic field B), and the geomagnetic indices Dst and Ap. Results. The cross-correlation analysis reveals a high degree of correlation between all studied parameters. In particular, we show that the Ap index is considerably more sensitive to HSS and CH characteristics than Dst. The Ap and Dst indices are most tightly correlated with the solar wind parameter BV 2 . Conclusions. From the point of view of space weather, the most important result is that the established empirical relationships provide a few-days-in-advance forecasting of the HSS characteristics and the related geomagnetic activity at the six-hour resolution.

Section: Discussionmentioning

confidence: 92%

Equatorial coronal holes, solar wind high-speed streams, and their geoeffectiveness

Vršnak

Veronig

et al. 2010

A&A

“…kugi.kyoto-u.ac.jp/dstae/index.html. For more detailed information about the indices, we refer to Prölss (2004b) and Verbanac et al (2010Verbanac et al ( , 2011. Among the available geomagnetic indices, these three indices have been chosen for describing the L PP as a function of geomagnetic activity because their variations can be physically interpreted and related to the specific magnetospheric current system (e.g., the ring current and polar electrojet).…”

Section: Annmentioning

confidence: 99%

The relationship between plasmapause, solar wind and geomagnetic activity between 2007 and 2011

Pierrard

Bandić³

et al. 2015

Ann. Geophys.

Abstract. Taking advantage of the Cluster satellite mission and especially the observations made by the instrument WHISPER to deduce the electron number density along the orbit of the satellites, we studied the relationships between the plasmapause positions (L PP ) and the following L PP indicators: (a) solar wind coupling functions B z (Z component of the interplanetary magnetic field vector, B, in GSM system), BV (related to the interplanetary electric field; B is the magnitude of the interplanetary magnetic field vector, V is solar wind velocity), and d mp /dt (which combines different physical processes responsible for the magnetospheric activity) and (b) geomagnetic indices Dst, Ap and AE. The analysis is performed separately for three magnetic local time (MLT) sectors (Sector1 -night sector (01:00-07:00 MLT); Sector2 -day sector (07:00-16:00 MLT); Sector3 -evening sector (16:00-01:00 MLT)) and for all MLTs taken together. All L PP indicators suggest the faster plasmapause response in the postmidnight sector. Delays in the plasmapause responses (hereafter time lags) are approximately 2-27 h, always increasing from Sector1 to Sector3. The obtained fits clearly resolve the MLT structures. The variability in the plasmapause is the largest for low values of L PP indicators, especially in Sector2. At low activity levels, L PP exhibits the largest values on the dayside (in Sector2) and the smallest on the postmidnight side (Sector1). Displacements towards larger values on the evening side (Sector3) and towards lower values on the dayside (Sector2) are identified for enhanced magnetic activity. Our results contribute to constraining the physical mechanisms involved in the plasmapause formation and to further study the still not well understood related issues.

“…ac.jp/dstdir/, and http://wdc.kugi.kyoto-u.ac.jp/ dstae/index.html, respectively. For more detailed information about the indices, we refer to Prolss (2004) and Verbanac et al (2011aVerbanac et al ( , 2010. Among the available geomagnetic indices, these three indices have been chosen for the evaluation of the geomagnetic activity since their variations can be physically interpreted and related to the specific current system, for example, the ring current and polar electrojet.…”

Section: Data Sets and Methodsmentioning

confidence: 99%

Comparison of geoeffectiveness of coronal mass ejections and corotating interaction regions

Živković

Vršnak

et al. 2013

A&A

Context. A detailed comparison of the geomagnetic responses to interplanetary coronal mass ejection (ICMEs) and corotating interaction regions (CIRs) during solar cycle 23 was performed using geomagnetic indices Dst, Ap, and AE. Aims. We aim to find out if there are relative differences in the response of various magnetospheric current systems to the impact of ICMEs and CIRs. In addition, we are exploring the possibility of forecasting geomagnetic activity using the coronagraphic observations of the ICME take-off. Methods. The peak values of the plasma characteristics of ICMEs and CIRs (velocity V, magnetic field B, and BV related to the electric field), and geomagnetic indices were investigated by applying the linear and power-law cross correlation analysis. The influence of the time-resolution on the results was performed for two time resolutions obtained by one-hour (three-hour for Ap) and six-hour data averaging. Results. For ICMEs the power-law fits are found to be important only for the relationships between BV and geomagnetic indices. For Ap and Dst, there is no difference between the one-hour (three-hour for Ap) and six-hour option. For AE, the one-hour data distribution shows more clearly the non-linear dependence on BV. Our data set shows that below BV ∼ 5 mV m −1 ICMEs have practically no geomagnetic effect at low and mid latitudes, but at high latitudes at least some geomagnetic activity will be triggered. For all HSS/CIRs dependencies, a power law is found to better describe the data than the linear fit. The data distributions show that BV has to reach ∼4 mV m −1 in order to drive at least some geomagnetic activity at all latitudes. We observed that there are fast CMEs that have almost no geomagnetic effect at low and mid latitudes. On the other hand, at high latitudes, fast CMEs always trigger some geomagnetic activity. This might be have implications for space weather forecasting. Conclusions. Magnetospheric response to both solar drivers (ICMEs and CIRs) is different at various latitudes, thus results in different development of various current systems within the Earth's magnetosphere and ionosphere. Furthermore, we show that ICMEs and CIRs cause different geomagnetic activity. In the case of ICMEs equatorial current system responses in a linear manner, while the response of the polar-current system is likely to be non-linear. For HSS/CIRs, apparently all current systems respond in a non-linear way, especially the polar current system.